Geology, Geochemistry And Genesis Of The Abra Lead-Copper Polymetallic Deposit, West Australia

Abstract:The Abra Lead-Copper polymetallic deposit is located from900Km NW of Perth, Western Australia. Tectonic setting of Abra deposit lies in the sub-basin of Bangemall basins--Mulgul Basin which was created by Capricorn orogenic belt, and is a very important polymetallic deposit in Bangemall ore concentration region. Wall rock is Irregully Formation in the Edmund Group cosisting of sandstone and siltstone. The lead-copper orebodies generally occur near the fractured belts and between the contact belt of lithology conversion.Analyzing the geological conditions of deposit, combining with the geochemical characteristics of this deposit, this paper focused on the material sources and ore-forming fluid in the formation of Abra Lead-Copper polymetallic deposit. Based on the above information, the genesis of this deposit is built, and the metallogenic model is initially established.Fluid inclusions study of quartz shows that ore-forming fluid is low temperature and moderate salinity. Hydrogen-Oxygen isotopes of quartz inclusions indicated that the ore-forming fluid is the mixture of metamorphic water and seawater. Rare earth element with positive Eu anomaly in ores and wall rocks reflects that the fluid in the ore-forming process suffered from a higher temperature and relative reduction surrounding.Sulfur isotopic analysis indicated that the sulfide is enriched in heavy sulfur, and the sulfur of ore-forming fluid is mainly derived from seawater, possibly sulfate reduction of sedimentary strata. The lead isotopes suggested that the lead of Abra deposit fall into the range of common lead. Projecting of lead on the tectonic evolution model diagram of Zartman Pb isotope indicated that material sources of ore-forming metals are from the upper crust.Re-Os dating of Pyrite from Abra Lead-Copper polymetallic deposit suggested there is a1329.5Ma isochron, which is nearly close to the ages of monazite1385±20Ma dated by using SHRIMP U-Pb. Geochronology result suggested that metallogenic epoch is Mesoproterozoic, and the mineralization lasted for a long time.According to the above studies, the Abra Lead-Copper polymetallic deposit formed in the Mesoproterozoic, and metamorphic water mixed with seawater made an vital contribution to the formation of the deposit. It is a typical epithermal lead-copper hydrothermal deposit hosted in sedimentary rocks.